VitDbol

Serum 25-hydroxyvitamin D [25(OH)D3] is a well-established marker for vitamin D status of the human body. However, there is significant inter-individual variation in the average serum 25(OH)D3 concentrations and also in the response to supplementation with vitamin D. Genetic and epigenetic factors have been suggested to be responsible for a large part of the variation, but currently there is little information about the health effects of the variation.

In our previous VitDmet study we showed that only half of the participants responded to the 5-month vitamin D3 supplementation of 40 µg/day or 80 µg/day as expected and that certain vitamin D receptor (VDR) target genes were suitable biomarkers for displaying the transcriptomic response of human tissues to vitamin D3 supplementation.

The purpose of the VitDbol study is to investigate whether a high-dose vitamin D3 oral bolus produces marked VDR target gene expression response and whether there is large inter-individual variation, as what was suggested with the 5-month lower-dose supplementation in VitDmet. From a part of the subjects, also epigenetic measurements are performed.

The study visits were carried out in the spring 2014 and 2015, when there is little UVB exposure in Finland. In the spring 2014, the subjects were randomized to receive either 2,000 micrograms (80 000 IU) of vitamin D3 (n=13) or placebo (n=8) in one day. Blood samples were collected for peripheral blood mononuclear cell isolation and serum 25(OH)D3 measurements at baseline and 24 h and 48 h and 30 days after the first dose. In February 2015, 14 new subjects were recruited in order to increase the size of the study. All the new subjects received the 2,000 microgram dose of vitamin D3, there were no new subjects in the placebo arm.

This study gives information whether it is possible to identify inter-individual differences in VDR target gene expression with a single large vitamin D3 dose. Identification of parameters that affect the inter-individual variability and response to supplementation in the serum 25(OH)D3 and whether these factors have an influence on the physiological effects of vitamin D will assist in establishing vitamin D requirements.